The iTunes Festival starts tonight and runs throughout the whole of September. The iPad app is free, as is every live performance. Artists performing this year include Muse, Alicia Keys, Elbow, Labrinth and One Direction, so there really is something for everyone this year.
What is particularly impressive is that all these performances can be streamed live directly to your iPad, iPhone, Apple TV (yes, Apple have made an app for that) or computer. We watched many of the live performances during last years iTunes Festival, the quality of the live video stream was particularly impressive.
If you don't have an Apple TV and want to watch the festival on your TV, don't forget you can connect your iPad to your HDMI equipped TV with Apple's AV connector or one of many third party connectors that do essentially the same thing but for less money.
App Store Link: iTunes Festival